Recently, the demand for portable electronic products such as notebooks, video cameras, cellular phones or the like has rapidly increased, and electric vehicles, energy storage batteries, robots, satellites have been actively developed. For this reason, high-performance secondary batteries allowing repeated charging and discharging are being actively studied.
Currently, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium secondary batteries, and the like are used as commercial secondary batteries. Among them, lithium secondary batteries have little to no memory effect in comparison with nickel-based secondary batteries, and thus lithium secondary batteries are gaining a lot of attention for their advantages of free charging or discharging, low self-discharging, and high energy density.
A lithium secondary battery generally uses lithium oxide and carbonaceous material as a positive electrode active material and negative electrode active material, respectively. The lithium secondary battery includes an electrode assembly in which a positive electrode plate and a negative electrode plate respectively coated with the positive electrode active material and the negative electrode active material are disposed with a separator being interposed between them, and an exterior, namely a battery case, which seals and accommodates the electrode assembly together with an electrolyte.
Generally, a lithium secondary battery may be classified into a can-type secondary battery where the electrode assembly is included in a metal can and a pouch-type battery where the electrode assembly is included in a pouch of an aluminum laminate sheet, depending on the shape of the exterior.
Recently, secondary batteries are widely used not only for small-sized devices such as cellular phones but also for middle-sized or large-sized devices such as vehicles and power storages. When secondary batteries are used for such middle-sized or large-sized devices, a great number of secondary batteries are electrically connected to enhance capacity and output. In particular, for such middle-sized or large-sized devices, pouch-type secondary batteries are frequently used since they can be easily accommodated and stacked.
The battery module may be regarded as a configuration where a lot of secondary batteries are connected in series or in parallel to enhance capacity and output. The battery module needs measurement of voltages of the secondary batteries in order to maintain performance stably. In order to measure voltages of the secondary batteries, the battery module includes bus bars connected to electrode leads of the secondary batteries and an ICB housing having wires for connecting the bus bars to an external measurement circuit.
Generally, an electrode lead and a bus bar are connected by means of laser welding. The laser welding is performed after the electrode lead and the bus bar are closely adhered to each other by compression using a compression jig. However, the wire electrically connected to the bus bar inevitably passes near the bus bar, and thus the wire is likely to be interposed between the compression jig and the ICB housing, which results in imperfect adhesion between the electrode lead and the bus bar. Therefore, in an existing battery module, bad welding may occur between the electrode lead and the bus bar, and the wire may be damaged due to the compression jig.